PROJECTSUMMARY Adolescenceisavulnerableperiodforinitiatingsubstanceuseandabuse,duringwhichtimesleepandcircadian rhythm disruptions are pervasive. It is increasingly recognized that sleep and circadian rhythm causally, and powerfullyregulaterewardprocessing,buttheunderlyingmechanismsremainpoorlyunderstood.Couldsleep and circadian rhythm traits be related to reward circuit function? Whether and how do sleep and circadian disruptionsleadtoincreasedvulnerabilityforsubstanceuseinadolescents?ThecentralhypothesisoftheCenter application is thatadolescentdevelopmentacts onunderlying sleepandcircadian traits to modifyhomeostatic sleep drive, circadian phase, and circadian alignment, which in turn impact cortico-limbic functions critical to substance use risk (e.g., rewardand cognitive control).It is furtherhypothesizedthat specific manipulationsof sleep and circadian rhythms during adolescence will affect reward responsivity and cognitive control in either positive or negative directions. This research project (Project 5) will focus on rodent models to determine the cellularandsynapticmechanismswithinthecortico-limbiccircuitthroughwhichsleepandcircadiandisruptions alterrewardprocessing.Specifically,thenucleusaccumbens(NAc)isareward-processing?hub?intheventral striatumwhichissensitivetobothsleepandcircadiandisruptions.Forexample,acutesleepdeprivationreduces glutamatereleaseatmedialprefrontalcortex-to-NAcmediumspinyprincipalneurons(MSNs)synapses;?chronic sleep fragmentation increases cholinergic neural activity in the NAc (preliminary results);? robust diurnal fluctuationsinAMPAreceptor(AMPAR)levelsandintrinsicmembraneexcitabilityarealsoobservedintheNAc MSNs,andcircadiangenemutationintheNAcleadstoalteredAMPARtransmissioninMSNs.Together,these resultssuggestthattheNAcmayrepresentaconvergingsiteforsleepandcircadianrhythmtoregulatereward processing.Accordingly,Project5willtestthehypothesisthatsleepandcircadianrhythmtargetaspectsofNAc synaptic transmission and neural modulation to regulate reward-motivated behaviors. Thus, Aim 1 will use genetically diverse outbred rats to determine whether naturally occurring ?early? and ?late? chronotypes are associated with different diurnal variationof AMPAR transmission in NAc MSNs. This aim will accommodate molecular (Project3)and behavioral (Project 4)characterizations of these rats. Aim2 will determine whether circadian disruptions without changes in sleep alter the diurnal variation of membrane excitability and/or postsynaptic AMPAR levels in the NAc MSNs. Aim 3 will determine the effects of acute and chronic sleep restrictionsonadenosineandcholinergictransmissionintheNAc,andthebehavioralconsequencesinnatural ordrugself-administration.TheexpectedoutcomeofProject5willintegrateandextendfindingsfrombehavioral (Project4)andmoleculargenetic(Project3)studies,whichtogetherwillprovidemechanisticinsightstoinform andfurtherdevelophumanstudies(Projects1&2).